FIG. 1 schematically illustrates a rear wheel drive vehicle powertrain and driver interface. Bold solid lines represent mechanical power flow connections such as shafts. Dashed lines represent the flow of information signals. For clarity, power flow paths and signals not impacted by the present invention may be omitted from FIG. 1. Engine 10 generates power by burning fuel. Starter 12 uses electrical energy from a battery to accelerate the engine to a speed at which the combustion process can be sustained. Transmission 14 establishes a variety of power flow paths with various speed and torque ratios between the engine crankshaft and a transmission output shaft to adapt the power to current vehicle needs. Specifically, transmission 14 is an automatic transmission in which a controller manages the engagement and disengagement of clutches and/or other measures to switch among available power flow paths and to adjust the transmission ratio. Differential 16 splits the power from the transmission output shaft between left and right rear wheels 18 and 20, permitting slight speed differences such as when the vehicle turns a corner. Front wheels 22 and 24 are not powered. A four wheel drive powertrain may include a transfer case which diverts some or all power from the transmission output shaft to the front wheels. A front wheel drive powertrain drives the front wheels as opposed to the rear wheels. In a front wheel drive powertrain, the transmission and differential may be combined into a single housing.
Brakes 26, 28, 30, and 32 selectively restrain wheels 18, 20, 22, and 24 respectively. Typically, the brakes are engaged in response to a driver depressing brake pedal 34. The torque capacity of the brakes varies in response to the degree of pedal depression and/or the force exerted on pedal 34. In some circumstances, some drivers may not be comfortable while pressing brake pedal 34 hard enough to slow the vehicle or to hold the vehicle stationary on an incline. To assist the driver, the braking system includes an engine driven brake boost 36. When the brake boost is available, the ratio of brake torque capacity to pedal force is increased.
Transmission 14 includes a park mechanism. A park mechanism is a mechanism designed to hold the vehicle stationary for an indefinite period without consuming any power. Typically, the park mechanism includes a park pawl which engages a park gear on the transmission output shaft. The park pawl is generally not designed to engage the park gear when the vehicle is moving at a speed higher than a relatively low threshold speed. The park mechanism may include features to delay engagement if the mechanism is triggered at a speed higher than the threshold speed.
A driver controls the operation of the powertrain by interacting with various controls. As discussed below, the driver controls the starting and stopping of the engine by manipulating ignition controls including keyfob sensor 38 and start/stop button 40. Keyfob sensor 38 determines whether an electronic keyfob is present within the vehicle, such as in a driver's pocket or purse. The driver selects the desired transmission range using a range selector 42. Range selector 42 may include buttons for various transmission modes such as buttons 44, 46, 48, and 50. Once a drive range is selected, the driver controls the wheel torque using accelerator pedal 52 (for positive torque) and brake pedal 34 (for negative torque). Controller 54 sends signals to control various powertrain components based on driver manipulation of the controls listed above and on other sensors. These other sensors may include a grade sensor 56 to detect the current incline (uphill or downhill) of the road. Display 57 is used to display messages to the driver. To avoid accidental release of the Park mechanism, the controller may not respond release the Park mechanism unless brake pedal 34 is depressed.